Significance and Use
5.1 The ring shear test is suited to the relatively rapid determination of drained residual shear strength because of the short drainage path through the thin specimen, and the capability of testing one specimen under different normal stresses to quickly obtain a shear strength envelope.
5.2 The test results are primarily applicable to assess the shear strength in slopes that contain a preexisting shear surface, such as old landslides, soliflucted slopes, and sheared bedding planes, joints, or faults.
5.3 The apparatus allows a reconstituted specimen to be overconsolidated and presheared prior to drained shearing. This simulates the field conditions that lead to a preexisting shear surface along which the drained residual strength can be mobilized.
5.4 The ring shear device keeps the cross-sectional area of the shear surface constant during shear and shears the specimen continuously in one rotational direction for any magnitude of displacement. This allows clay particles to become oriented parallel to the direction of shear and a residual strength condition to develop.
1.1 This test method provides a procedure for performing a torsional ring shear test under a drained condition to determine the residual shear strength of cohesive soils. An intact specimen can be used for testing. However, obtaining a natural slip surface specimen, determining the direction of field shearing, and trimming and aligning the usually non-horizontal shear surface in the ring shear apparatus is difficult. As a result, this test method focuses on the use of a reconstituted specimen to measure the residual strength. This test method is performed by deforming a presheared, reconstituted specimen at a controlled displacement rate until the constant drained shear resistance is offered on a single shear plane determined by the configuration of the apparatus. An unlimited amount of continuous shear displacement can be achieved to obtain a residual strength condition. Generally, three or more normal stresses are applied to a test specimen to determine the drained residual failure envelope. A separate test specimen may be used for each normal stress.
1.2 A shear stress-displacement relationship may be obtained from this test method. However, a shear stress-strain relationship or any associated quantity, such as modulus, cannot be determined from this test method because soil extrusion and volume change prevents defining the height needed in the shear strain calculations. As a result, shear strain cannot be calculated but shear displacement can be calculated.
1.3 The selection of normal stresses and determination of the shear strength envelope for design analyses and the criteria to interpret and evaluate the test results are the responsibility of the engineer or office requesting the test.
1.4 The values stated in SI units are to be regarded as standard. The values given in parentheses are mathematical conversions to inch-pound units that are provided for information only and are not considered standard.
1.5 All measured and calculated values shall conform to the guidelines for significant digits and rounding established in Practice D6026.